The present invention relates to composite articles having at least partially mechanically joined members such as airfoils of turbomachinery blades, vanes, struts, and the like, and more particularly to a fiber reinforced composite fastener suitable for attaching composites to composites or attaching composites to metals.
Increasing usage of composite material in aircraft secondary and primary structure has focused attention on enhancement of general quality and long-term maintainability while retaining light weight. Composite airfoils, often hollow with various designs of reinforcing structure therein, utilize a variety of composite material including graphite/epoxies, graphite/glass/epoxies, and like fiber-reinforced composite material. When one member of the structure is metallic, the potential for galvanic corrosion is extremely high; aluminum fasteners and even stainless steel fastening systems can be affected. Thus, titanium fasteners frequently are specified.
Composite fasteners for composite airfoil assemblies have been the subject of prior development Droprams. For example, injection molded fiber-reinforced thermoplastic rivets and bolts were evaluated in a U.S. Air Force program reported in Report AFML-TR-79-4044, Project IR-453-7(1), June, 1979. The short fiber reinforcement, however, limited the tensile properties of such preformed thermoplastic rivets. Thus, there still is a need for development of simple composite fasteners of improved mechanical properties for joining composite to composite material or joining composite to metallic material in the formation of airfoils and other aircraft structures. The present invention is addressed to such need.